CN107735161B

CN107735161B - NOx adsorbent catalysts, methods and systems

Info

Publication number: CN107735161B
Application number: CN201680025336.0A
Authority: CN
Inventors: G·格鲁贝特; T·纽鲍尔; A·H·彭克; M·希尔真多夫; Y·李
Original assignee: BASF Corp
Current assignee: BASF Corp
Priority date: 2015-03-03
Filing date: 2016-03-03
Publication date: 2021-05-04
Anticipated expiration: 2036-03-03
Also published as: US10493434B2; JP7055635B2; CA2978703A1; KR20170128408A; RU2017134081A; WO2016141140A1; CN107735161A; EP3265212A1; JP2022002847A; JP7279127B2; US20180043335A1; BR112017018826A2; JP2018517541A; RU2017134081A3; KR102609702B1; EP3265212A4; MX2017011250A

Abstract

A lean burn engine exhaust gas treatment article comprising a low temperature lean _NOx trap (LT-LNT) composition and method of use is disclosed. Also disclosed is a lean burn engine exhaust treatment system including a lean burn engine exhaust treatment article. The low temperature lean _NOx trap (LT-LNT) composition may comprise a washcoat on the support substrate, the washcoat comprising a platinum group metal component impregnated on a first support material comprising at least 50% alumina. The washcoat layer may further comprise a low temperature _NOx storage material comprising a bulk particulate reducible metal oxide. A method of monitoring the aging state of a lean burn oxidation catalyst in a lean burn engine catalyst system is also disclosed.

Description

NOxSorbent catalyst, method and system

Technical Field

The invention relates to a method for producing a fuel cell containing low-temperature lean NO_xLean burn engine exhaust treatment articles of trap (LT-LNT) compositions and methods of use thereof. The invention also relates to a lean burn engine exhaust treatment system comprising the lean burn engine exhaust treatment article. More particularly, the present invention relates to low temperature NO-lean washcoat layers comprising a washcoat layer on a carrier substrate_xA trap (LT-LNT) composition, the washcoat comprising an impregnation comprising at least 50% oxygenA platinum group metal component on a first support material of aluminum. The washcoat layer may further include low temperature NO_xA storage material comprising a bulk particulate reducible metal oxide. The invention also relates to a method of monitoring the aging status of a lean burn oxidation catalyst in a lean burn engine catalyst system.

Background

Engines, including diesel engines, are designed to operate under lean conditions as a fuel economy consideration. Such future engines are referred to as "lean burn engines". That is, the air-fuel ratio in the combustion mixture provided to such engines is maintained significantly above stoichiometric (e.g., an air-fuel weight ratio of 18: 1) such that the resulting exhaust gas is "lean", i.e., the oxygen content of the exhaust gas is relatively high. Although lean-burn engines provide improved fuel economy, they suffer from the disadvantage that conventional three-way catalytic converters (TWCs) are not effective at reducing NO in such engines due to excessive oxygen in the exhaust gas_xAnd (5) discharging. Attempts to overcome this problem include the use of NO_xAnd (4) a trap. The exhaust gas of such engines is used for storing NO during lean (oxygen-rich) operation_xAnd release stored NO during rich (fuel-rich)) operation_xCatalyst of (2)/NO_xAnd (5) treating the sorbent. catalyst/NO during rich (or stoichiometric) operation_xCatalyst component of sorbent for passing NO_x(including from NO)_xNO released by sorbents_x) NO promotion by reaction with Hydrocarbons (HC), carbon monoxide (CO) and/or hydrogen present in the exhaust gas_xIs reduced to nitrogen.

Diesel engines provide better fuel economy than gasoline engines and typically run 100% of the time under lean conditions where it is difficult to reduce NO due to the presence of excess oxygen_x. In this case, catalyst/NO_xSorbents for storing NO_xIs effective. In NO_xAfter storage mode, transient rich conditions must be used to release/reduce stored NO_xTo nitrogen.

In a reducing environment, lean in NO_xTrap (LNT) by promoting steam reforming reaction and water gas of hydrocarbonsRotation (WGS) reaction to activate the reaction to provide H₂As reducing agents for reducing NO_x. The water gas shift reaction is a chemical reaction in which carbon monoxide reacts with steam to form carbon dioxide and hydrogen. The presence of ceria in the LNT catalyzes the WGS reaction, improving LNT to SO₂The inactivation resists and stabilizes the PGM.

The lean operating cycle is typically between 1 minute and 20 minutes, and the rich operating cycle is typically short (1-10 seconds) to keep as much fuel as possible. To increase NO_xConversion efficiency, short and frequent regeneration is advantageous over long but less frequent regeneration.

LNT catalysts operate under cyclic lean (trap mode) and rich (regeneration mode) exhaust conditions during which engine-out NO is converted to N₂As shown in equations 1-6:

lean conditions: 2NO + O₂→2NO₂ (1)

(trap mode) 4NO₂+2MCO₃+O₂→2M(NO₃)₂+2CO₂ (2)

Rich conditions: m (NO)₃)₂+2CO→MCO₃+NO₂+NO+CO₂ (3)

(regeneration mode) NO₂+CO→NO+CO₂ (4)

2NO+2CO→N₂+2CO₂ (5)

2NO+2H₂→N₂+2H₂O (6)

In order to prepare the emerging European Union 6 automobile exhaust emission catalyst market for meeting the increasingly stringent NO requirements_xEmission, Diesel Oxidation Catalyst (DOC) for diesel passenger cars may be replaced with a tightly coupled lean NO lean with diesel oxidation functionality_xTrap for a motor displacement of 1.2 to 2.5L. Except for managing NO of vehicle_xIn addition to emissions, this change would require the LNTDOC to effectively oxidize engine-out Hydrocarbon (HC) and carbon monoxide (CO) emissions. Specifically, this change requires the LNT to satisfy the NO requirement_xConversion to N₂By NO removal_xFunction and simultaneously undertake DOC oxidation engineThe exhausted Hydrocarbons (HC) and carbon monoxide (CO) (equations 7 and 8) and the dual role of generating the exotherm for regenerating the Catalyzed Soot Filter (CSF).

HC and CO Oxidation C_xH_y+O₂→CO₂+H₂O (7)

2CO+O₂→2CO₂ (8)

New legislation, such as the diesel EU 6b and 6c legislation, requires the reduction of carbon dioxide (CO)₂) And (5) discharging. To comply with these legislations, engine calibration for light-duty diesel applications must be implemented to reduce carbon dioxide emissions. In fact, in the drive cycle of a vehicle using such a catalyst, the reduction in carbon dioxide emissions will result in lower temperatures in front of the carbon monoxide (CO) and Hydrocarbon (HC) oxidation catalyst. For having NO stored before SCR ignition_xTo produce lower NO_xDischarged lean NO_xSystems of trap (LT-LNT) compositions, stored NO_xAnd conversion to N at lower temperatures₂Is a challenge.

Furthermore, in some countries, new on-board diagnostics (OBD) regulations require that Diesel Oxidation Catalyst (DOC) functions (mainly HC conversions) in DOC-SCR systems are detected while driving. Currently, there is no operating DOC detection method that can detect the DOC aging state because there is no existing HC sensor. Accordingly, it is desirable to provide DOC compositions capable of providing OBD capabilities.

Disclosure of Invention

A first embodiment relates to a lean burn engine exhaust gas treatment article comprising a low temperature NO lean washcoat on a carrier substrate_xA trap (LT-LNT) composition, the washcoat comprising a platinum group metal component impregnated on a first layer of support material comprising at least 50% alumina, the washcoat further comprising low temperature NO comprising a bulk particulate reducible metal oxide_xThe material is stored.

According to a second embodiment, the first embodiment is modified such that the first support material comprises 100% alumina.

According to a third embodiment, the first embodiment is modified such that the reducible metal oxide material comprises 100% ceria.

According to a fourth embodiment, the first embodiment is modified such that the first support material consists essentially of ceria and alumina.

According to a fifth embodiment, the fourth embodiment is modified such that the first support material comprises 20-50 wt.% ceria and 50-80 wt.% alumina.

According to a sixth embodiment, either of the fourth and fifth embodiments is modified such that the ceria and alumina are present at a ceria to alumina ratio of 30: 70.

According to a seventh embodiment, any one of the third to sixth embodiments is modified such that ceria and alumina are present at a ceria to alumina ratio of 50: 50.

According to an eighth embodiment, any one of the first to seventh embodiments is modified such that the reducible metal oxide is CeO₂、MnO₂、Mn₂O₃、Fe₂O₃One or more of CuO or CoO, and mixtures thereof.

According to a ninth embodiment, any one of the first to eighth embodiments is modified such that the first support material further comprises one or more dopants selected from oxides of La, Zr, Nb, Pr, Y, Nd or Sm.

According to a tenth embodiment, any one of the first to ninth embodiments is modified such that the platinum group metals are platinum and palladium.

According to an eleventh embodiment, any of the first through tenth embodiments are modified such that the washcoat layer further comprises Rh on a second support material comprising a reducible metal oxide, alumina, zirconia, and mixtures thereof.

According to a twelfth embodiment, any of the first to eleventh embodiments is modified such that the second support material comprises 5 to 50 wt.% of zirconia and greater than 50 wt.% of reducible metal oxide.

According to a thirteenth embodiment, any of the first through twelfth embodiments are modified such that the reducible metal oxide is ceria, wherein the alumina and ceria are present in the LT-LNT composition at an alumina to ceria ratio of 4:1 to 1:3, more specifically 1:1 to 1:3, even more specifically 1:1 to 1: 2.

According to a fourteenth embodiment, any of the first through thirteenth embodiments are modified such that the LT-LNT composition is disposed as a washcoat on a substrate, the alumina is at 1 to 4g/in³More specifically 1 to 3g/in³A range of (a) exists.

According to a fifteenth embodiment, any one of the first to fourteenth embodiments is modified such that Pt is at 20 to 200g/ft³In the range of 1 to 50g/ft of palladium³And Rh is present in a range of 0 to 20g/ft³Is present on the second support. According to a sixteenth embodiment, any one of the first to fourteenth embodiments is modified such that the platinum is at 20 to 200g/ft³In the range of 4 to 30g/ft of palladium³And Rh is present in a range of 2 to 10g/ft³Is present on the second support. According to a seventeenth embodiment, any one of the first to fourteenth embodiments is modified such that Pt is at 20 to 200g/ft³In the range of 5 to 20g/ft of palladium³And Rh is present in a range of 3 to 7g/ft³Is present on the second support.

According to an eighteenth embodiment, any one of the first to fourteenth embodiments is modified such that Pt is at 40 to 150g/ft³In the range of 1 to 50g/ft of palladium³And Rh is present in a range of 0 to 20g/ft³Is present on the second support. According to a nineteenth embodiment, any one of the first to fourteenth embodiments is modified such that Pt is at 40 to 150g/ft³In the range of 4 to 30g/ft of palladium³And Rh is present in a range of 2 to 10g/ft³Is present on the second support. According to a twentieth embodiment, any one of the first to fourteenth embodiments is modified such that Pt is at 40 to 150g/ft³In the range of 5 to 20g/ft of palladium³And Rh is present in a range of 4 to 7g/ft³Is present on a second support。

According to a twenty-first embodiment, any one of the first to fourteenth embodiments is modified such that Pt is at 60 to 130g/ft³In the range of 1 to 50g/ft of palladium³And Rh is present in a range of 0 to 20g/ft³Is present on the second support. According to a twenty-second embodiment, any one of the first to fourteenth embodiments is modified such that Pt is at 60 to 130g/ft³In the range of 4 to 30g/ft of palladium³And Rh is present in a range of 2 to 10g/ft³Is present on the second support. According to a twenty-third embodiment, any one of the first to fourteenth embodiments is modified such that Pt is at 60 to 130g/ft³In the range of 5 to 20g/ft of palladium³And Rh is present in a range of 4 to 7g/ft³Is present on the second support.

According to a twenty-fourth embodiment, any of the first through twenty-third embodiments is modified such that the LT-LNT composition is free of barium and other alkaline earth metals.

According to a twenty-fifth embodiment, a lean burn engine exhaust gas treatment system comprises the lean burn engine exhaust gas treatment article of any one of the first to twenty-fourth embodiments, wherein the system further comprises a downstream Selective Catalytic Reduction (SCR) catalyst.

According to a twenty-sixth embodiment, the twenty-fifth embodiment is modified such that the LT-LNT composition is disposed as a washcoat on a substrate and the SCR catalyst is disposed as a separate washcoat on a separate downstream substrate.

According to a twenty-seventh embodiment, any of the twenty-fifth to twenty-sixth embodiments are modified such that the LT-LNT composition is on a honeycomb flow-through substrate and the SCR catalyst is on a wall-flow substrate. The SCR catalyst may also be coated on a flow-through or wall-flow filter.

According to a twenty-eighth embodiment, any of the twenty-fifth to twenty-sixth embodiments are modified such that the LT-LNT composition is on a wall-flow substrate and the SCR catalyst is on a honeycomb flow-through substrate.

According to a twenty-ninth embodiment, any of the first through twenty-eighth embodiments are modified such that the LT-LNT composition further comprises 1-10 wt.% of an alkaline earth metal selected from Mg, Ca, Sr, and Ba.

According to a thirty-third embodiment, the catalytic article of any one of the first through twenty-fourth and twenty-ninth embodiments can be used in an exhaust system of a lean-burn internal combustion engine.

According to a thirty-first embodiment, the catalytic article of any one of the first through twenty-fourth and twenty-ninth embodiments can be used in a lean-burn engine exhaust gas treatment system further comprising a lambda sensor downstream of the LT-LNT.

In a thirty-second embodiment, the thirty-second embodiment is modified such that the system further comprises a second lambda sensor located upstream of the LT-LNT, and the lambda sensor and the second lambda sensor are in communication with an on-board diagnostic system that correlates a degradation in oxygen storage capacity of the LT-LNT to a decrease in HC conversion rate on the LT-LNT.

According to a thirty-third embodiment, there is provided a method of monitoring aging of a lean-burn oxidation catalyst in a lean-burn engine catalyst system, the method comprising: passing a lean burn engine exhaust stream through the exhaust treatment article of any of the first through twenty-fourth and twenty-ninth through thirty-third embodiments, wherein the method further comprises measuring degradation of the LT-LNT composition located in the exhaust flow path; and correlating the degradation of the LT-LNT composition to a decrease in hydrocarbon conversion efficiency of the lean oxidation catalyst.

According to a thirty-fourth embodiment, the thirty-third embodiment is modified such that the step of measuring the degradation of the LT-LNT composition comprises monitoring at 250 ℃ with a lambda sensor upstream of the LT-LNT and a second lambda sensor downstream of the LT-LNT_xH in exhaust gas stream during cleaning₂And (4) content.

According to a thirty-fifth embodiment, the thirty-third embodiment is modified such that the step of measuring the degradation of the LT-LNT composition comprises using NH downstream of the LT-LNT₃Sensors monitor NH in exhaust flow during rich purge₃And (4) content.

According to a thirty-sixth embodiment, a thirty-third embodimentThe step modified such that measuring the degradation of the LT-LNT composition comprises using NO during a lean period following a rich purge_xSensor monitoring of NO_xAnd (5) storing.

According to a thirty-seventh embodiment, the thirty-third embodiment is modified such that the step of measuring the degradation of the LT-LNT composition comprises measuring the degradation of the LT-LNT composition in the NO_xWith NO during rich purge after storage phase_xSensor monitoring of NO_xAnd (4) slipping.

Drawings

FIG. 1 shows the average NO of the LT-LNT of the invention and the prior art LNT over the last 5 cycles of the 7-cycle lean-rich test_xComparison of conversion.

FIG. 2 shows the average NO of the LT-LNT of the invention and the prior art LNT during rich for the last 5 cycles of the 7-cycle lean-rich test_xComparison of emissions.

FIG. 3 shows the CO performance of a LT-LNT with Pt/Pd impregnated on ceria compared to a corresponding LT-LNT with Pt/Pd impregnated on alumina support.

FIG. 4 shows HC performance of a LT-LNT with Pt/Pd impregnated on ceria compared to a corresponding LT-LNT with Pt/Pd impregnated on alumina support.

FIG. 5 shows the average NO of the LT-LNT of the invention and the prior art LNT over the last 5 cycles of the 7-cycle lean-rich test_xAnd (4) conversion rate.

FIG. 6 shows the average NO of the LT-LNT of the invention and the prior art LNT over the last 5 cycles of the 7-cycle lean-rich test_xAnd (4) conversion rate.

Detailed Description

Before describing several exemplary embodiments of the invention, it is to be understood that the invention is not limited to the details of construction or process steps set forth in the following description. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.

According to one or more embodiments of the present invention, there is provided a low temperature lean NO_xTrap (LT-LNT) compositions. In one aspect, according to one or more embodiments, the LT-LNT composition provides NO in addition to NO₂High conversion rate ofIn addition, NO enrichment at standard LNT_xThe events are followed by relatively low CO and HC light-off temperatures, which are required by downstream SCR catalysts. The downstream SCR catalyst can be on a flow-through substrate or on a wall-flow filter substrate.

In one or more embodiments, the low temperature lean NO_xA trap (LT-LNT) composition comprises a washcoat layer on a support substrate, the washcoat layer comprising a platinum group metal component impregnated on a first support material, the first support material comprising at least 50% alumina. In one or more embodiments, the washcoat layer can further include low temperature NO_xA storage material comprising a bulk particulate reducible metal oxide. Also provided, in accordance with one or more embodiments of the present invention, are lean burn engine exhaust gas treatments including lean burn engine exhaust gas treatment articles comprising low temperature lean NO and methods of using the same_xTrap (LT-LNT) compositions. Methods for monitoring the aging state of a lean burn oxidation catalyst in a lean burn engine catalyst system are also provided according to one or more embodiments of the invention.

It has been found that low temperature lean NO as disclosed herein is comprised_xLean burn engine exhaust treatment article of trap (LT-LNT) composition rich in NO at standard LNT_xHaving very low carbon monoxide (CO) and Hydrocarbon (HC) ignition after an event, and high NO to NO₂An oxidation function, which is required for high Selective Catalytic Reduction (SCR) performance. For low temperature lean NO disclosed herein_xTrap (LT-LNT) composition, rich in NO_xHigh CO and HC performance was also observed afterwards.

Furthermore, it has been found that the catalytic compositions disclosed according to one or more embodiments may have downstream sensors such as λ, H₂，NH₃，NO_xEtc. to provide on-board diagnostic functionality.

With respect to the terms used in this disclosure, the following definitions are provided.

By "support" in reference to a washcoat layer is meant a material that receives a noble metal, stabilizer, dopant, adjuvant, binder, etc., by association, dispersion, impregnation, or other suitable means. Useful catalyst supports can be made from high surface area refractory oxide supports. Useful high surface area supports include one or more refractory oxides selected from the group consisting of alumina, titania, silica and zirconia. These oxides include, for example, silica and metal oxides such as alumina, including mixed oxide forms such as silica-alumina, aluminosilicates which may be amorphous or crystalline, alumina-zirconia, alumina-chromia, alumina-ceria and the like. The support consists essentially of alumina, which preferably comprises members of the gamma or activated alumina family, such as gamma and eta alumina, and small amounts of other refractory oxides, if present, e.g., about up to 20 wt.%.

The term "alkaline earth metal" as used herein refers to one or more chemical elements defined in the periodic table of elements, including beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra). In one or more embodiments, the alkaline earth metal component comprises a barium component. In a particular embodiment, the barium is applied as barium oxide. The alkaline earth metal component may be present in the washcoat in a range of about 0.5% to 10% by weight on an oxide basis. In particular embodiments, the alkaline earth metal component comprises magnesium and barium components. In particular embodiments, the alkaline earth metal component comprises a barium component. In a very specific embodiment, the alkaline earth metal component comprises a barium component in an amount of about 0.5 wt.% to about 2 wt.% on an oxide basis.

The term "platinum group metal" or "PGM" as used herein refers to one or more chemical elements defined in the periodic table of elements, including platinum, palladium, rhodium, osmium, iridium, and ruthenium, and mixtures thereof. In one or more embodiments, the platinum group metal is selected from the group consisting of platinum, palladium, rhodium, iridium, and mixtures thereof. In one embodiment, the platinum group metal is selected from the group consisting of platinum, palladium, rhodium and mixtures thereof. It will be apparent to those skilled in the art that the platinum group metal component as a catalyst may be present in the catalyst in a variety of oxidation states at the time of use. For example, the palladium component may be present in the catalyst as palladium metal, pd (ii) and pd (iv). Depending on one method of preparing the catalyst, dispersion of the catalytic component on a support, such as activated alumina support particles, may be achieved using a platinum group metal component, such as a suitable compound and/or complex of a platinum group metal. As used herein, the term "platinum group metal component" refers to any platinum group metal compound, complex, or the like that decomposes or otherwise converts to a catalytically active form (typically a metal or metal oxide) upon calcination or use of a catalyst. Water-soluble or water-dispersible compounds or complexes of the platinum group metals may be used so long as the liquid in which the catalytic metal compound is impregnated or deposited on the support particles does not adversely react with the catalytic metal or its compound or complex or other components of the catalyst composition and is capable of being removed from the catalyst by volatilization or decomposition upon heating and/or application of a vacuum. In some cases, the liquid cannot be completely removed until the catalyst is placed into service and subjected to the high temperatures encountered during operation. Generally, aqueous solutions of soluble compounds of the platinum group metals are preferred from economic and environmental points of view. For example, suitable compounds are chloroplatinic acid, amine-solubilized platinum hydroxide, palladium nitrate or chloride, rhodium nitrate, hexamine rhodium chloride, and the like. These compounds are converted to catalytically active forms of the platinum group metals or compounds thereof during the calcination step, or at least during the initial stages of use of the catalyst.

Embodiments of the first aspect of the invention relate to a composition comprising low temperature lean NO_xLean burn engine exhaust treatment articles of trap (LT-LNT) compositions. In one or more embodiments, the low temperature lean NO_xA trap (LT-LNT) composition comprises a washcoat layer on a support substrate, the washcoat layer comprising a platinum group metal component impregnated on a first support material comprising at least 50% alumina. In one or more embodiments, the first support material comprises 100% alumina. In one or more embodiments, the first support material consists essentially of ceria and alumina. In one or more embodiments, the first support material comprises 20 to 50 wt.% ceria and 50 to 80 wt.% alumina. In one or more embodiments, the ceria and alumina are present at a 30:70 ceria to alumina ratio. At one isIn one or more embodiments, the ceria and alumina are present at a 50:50 ceria to alumina ratio.

The washcoat also includes low temperature NO_xA storage material comprising a bulk particulate reducible metal oxide. In one or more embodiments, the reducible metal oxide is CeO₂，MnO₂，Mn₂O₃， Fe₂O₃CuO or CoO. In one or more embodiments, the reducible metal oxide is 100% ceria. According to one or more embodiments, the platinum group metal is not directly impregnated in the low temperature NO containing the bulk particulate reducible metal oxide_xOn the storage material. In one or more embodiments, the platinum group metals include platinum and palladium. In one or more embodiments, the low temperature lean NO_xTrap (LT-LNT) composition at least one layer of low temperature lean NO_xThe trap (LT-LNT) composition comprises Pt or Pt/Pd on alumina together with a bulk particulate reducible metal oxide. In one or more embodiments, the bulk particulate reducible metal oxide is ceria. In one or more embodiments, where the bulk particulate reducible metal oxide is ceria, the ceria particles are mixed with the activated alumina particles such that the ceria is present in solid or bulk form, rather than impregnating the alumina particles, for example, with a solution of a ceria compound (which upon calcination is converted to ceria disposed within the alumina particles). In one or more very specific embodiments, the first support is doped with one or more oxides of Y, Nd, Sm, Zr, Nb, La, and Pr. In one or more embodiments, the first support material may also include alumina and dopants, including but not limited to oxides of Y, Nd, Sm, Zr, La, Nb, and Pr.

In one or more embodiments, the first support material and low temperature NO comprising bulk particulate reducible metal oxide_xThe memory material has different compositions. In other embodiments, the first support material and low temperature NO comprising bulk reducible metal oxide_xThe memory materials have the same composition.

As noted above, the platinum group metal may be selected from platinum, palladium, rhodium, iridium and mixtures thereof. In one embodiment, the platinum group metal is selected from platinum, palladium and mixtures thereof. In a more specific embodiment, the platinum group metal is selected from the group consisting of platinum, palladium, rhodium and mixtures thereof. In one or more embodiments, the platinum group metal component includes one or more of Pt and Pd. In one or more specific embodiments, the platinum group metal component comprises Pt and Pd.

In one or more embodiments, the washcoat layer further comprises Rh on the second support material. In one or more embodiments, Rh is present at 0 to 20g/ft³Is present on the second support. In one or more embodiments, Rh is present at 2 to 10g/ft³Is present on the second support. In one or more embodiments, Rh is present at 3 to 7g/ft³Is present on the second support. In one or more embodiments, the washcoat layer further comprises Rh comprising a reducible metal oxide, alumina, and a compound derived from zirconium, preferably zirconia, on a second support material. The zirconium compound may be provided as a water soluble compound such as zirconium acetate or as a relatively insoluble compound such as zirconium hydroxide, both of which are converted to oxides upon calcination. Should be present in sufficient quantity to enhance the stability and acceleration of the catalytic washcoat composition. In particular embodiments, the second support material comprises from 50 to 95 weight percent reducible metal oxide and from 5 to 50 weight percent zirconia.

In one or more embodiments, the second support material consists essentially of ceria and alumina. In one or more embodiments, the second support material comprises 20 to 50 wt.% ceria and 50 to 80 wt.% alumina. In one or more embodiments, the second support material comprises ceria and alumina at a ceria to alumina ratio of 30: 70. In one or more embodiments, the second support material comprises ceria and alumina at a ceria to alumina ratio of 50: 50. In one or more specific embodiments, the refractory metal oxide on the second support is doped with one or more oxides of Mg, Mn, and Zr. In one or more very specific embodiments, the refractory metal oxide is doped with one or more oxides of Mg and Zr.

In one or more embodiments, the reducible metal oxide is ceria, and the alumina and ceria are present in the LT-LNT composition at an alumina to ceria ratio of 4:1 to 1: 4. In one or more specific embodiments, the alumina and ceria are present in the LT-LNT composition at an alumina to ceria ratio of 1:1 to 1: 4. In one or more very specific embodiments, the alumina and ceria are mixed in a ratio of 1:1 to 1:3 alumina: the ceria ratio is present in the LT-LNT composition. In one or more embodiments, the LT-LNT composition is disposed on the substrate as a washcoat layer with alumina at 1 to 4g/in³A range of (a) exists.

In one or more embodiments, the LT-LNT composition is free of barium and other alkaline earth metals. In one or more embodiments, the LT-LNT composition can further comprise 1-10 wt.% of a barium compound.

Generally, the low temperature lean NO of the present invention_xA trap (LT-LNT) composition is disposed on the substrate. The substrate may be any of those materials commonly used to prepare catalysts, and typically comprises a ceramic or metal honeycomb structure. Any suitable substrate may be used, for example a monolithic substrate having fine parallel gas flow channels extending therethrough from an inlet or outlet face of the substrate, such that the channels are open to fluid flow (referred to herein as a flow-through substrate). The channels, which are essentially straight paths from their fluid inlets to their fluid outlets, are defined by walls on which the catalytic material is coated as a washcoat, such that the gases flowing through the channels contact the catalytic material. The flow channels of the monolithic matrix are thin-walled channels that can have any suitable cross-sectional shape and size, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, elliptical, circular, and the like.

Lean NO according to embodiments of the invention_xThe trap wash coating composition may be applied to the substrate surface by any method known in the art. For example, the catalyst washcoat can be applied by spraying, powder coating or brushing or dipping the surface into the catalyst composition.

Low temperature lean NO as disclosed herein_xThe rich activation duration of one or more embodiments of the trap (LT-LNT) composition is significantly shorter than a standard LNT and can be used at lower temperatures. Low temperature lean NO compared to standard LNT_xOne or more embodiments of the trap (LT-LNT) composition may remove stored sulfur at lower temperatures. At low temperature lean in NO_xIn one or more embodiments of the trap (LT-LNT) composition, NO_xThermal desorption between 200 ℃ and 300 ℃ which ensures low temperature lean NO when the engine is stopped_xTrap (LT-LNT) giving high NO for the next start_xAnd (4) adsorbing.

Low temperature lean NO according to embodiments of the invention compared to currently available Pt/Pd DOC and LT-LNT technologies_xTrap (LT-LNT) compositions offer high CO and HC performance, and also have significant PGM cost reduction potential.

Low temperature lean NO as described herein_xA trap (LT-LNT) composition comprises a washcoat layer comprising a platinum group metal component impregnated on a first support material comprising at least 50% alumina, and further comprising low temperature NO comprising a bulk particulate reducible metal oxide_xThe washcoat layer of the storage material may be incorporated into the DOC as an additional washcoat layer along with the DOC washcoat layer, which will be referred to herein as a LT-LNT/DOC catalyst. Alternatively, the low temperature lean NO as described herein_xA trap (LT-LNT) composition can be incorporated as part of the active DOC washcoat to provide a LT-LNT/DOC catalyst.

Another aspect of the invention relates to the use of the low temperature lean NO as described herein_xA system of trap (LT-LNT) compositions. In one embodiment of the system, the low temperature lean NO is provided on a first substrate_xA trap (LT-LNT) composition, and a Selective Catalytic Reduction (SCR) catalyst is provided downstream of the LT-LNT composition. The SCR catalyst can be disposed on a flow-through honeycomb substrate or a wall-flow substrate. The LT-LNT composition may be provided on a flow-through honeycomb substrate or on a wall-flow substrate.

Suitable SCR catalyst compositions for use in the system are effective to catalyze NO_xReduction of components even at normal and low exhaust gas temperaturesSufficient NO can be treated even under low load conditions of degree dependence_xAnd (4) horizontal. In one or more embodiments, the catalyst article is capable of converting at least 50% of NO_xConversion of component into N₂Depending on the amount of reducing agent added to the system. In addition, the SCR catalyst composition used in the system is also desirably capable of assisting in the regeneration of the filter by lowering the temperature at which the soot fraction of the particulate matter combusts. Another desirable characteristic of the composition is that it has catalytic O₂With any excess of NH₃To N₂To H₂O capacity of NH₃Is not vented to the atmosphere.

The SCR catalyst composition should be resistant to degradation when exposed to sulfur components that are typically present in diesel exhaust compositions and should have acceptable hydrothermal stability consistent with the desired regeneration temperature.

Suitable SCR catalyst compositions are described, for example, in U.S. patent 5,300,472('472 patent), 4,961,917('917 patent), and 5,516,497('497 patent), which are incorporated herein by reference in their entirety. The composition disclosed in the' 472 patent includes, in addition to titanium dioxide, at least one oxide of tungsten, silicon, boron, aluminum, phosphorus, zirconium, barium, yttrium, lanthanum, or cerium, and at least one oxide of vanadium, niobium, molybdenum, iron, or copper. The composition disclosed in the' 917 patent comprises one or both of iron and copper promoters present in the zeolite in an amount of about 0.1 to 30 weight percent, with specific examples being about 1 to 5 weight percent, based on the total weight of promoter plus zeolite. Except that they catalyze NO_xAnd NH₃Reduction to N₂In addition to the ability of (a), the disclosed compositions can also promote excess NH₃And O₂Especially for compositions with higher promoter concentrations. In a specific embodiment, the SCR catalyst comprises a molecular sieve. In various embodiments, the molecular sieve may have a zeolite framework, and the zeolite framework may have a ring size of no greater than 12. In one or more embodiments, the zeolitic framework material comprises double hexacyclic (d6r) units.

In one or more embodiments, the zeolitic framework material may be selected from AEI, AFT, AFX, CHA, EAB, EMT, ERI, FAU, GME, JSR, KFI, LEV, LTL, LTN, MOZ, MSO, MWW, SAS, SAT, SAV, SBS, SBT, SFW, SSF, SZR, TSC, WEN, and combinations thereof. In various embodiments, the zeolitic framework material may be selected from AEI, CHA, AFX, ERI, KFI, LEV, and combinations thereof. In various embodiments, the zeolitic framework material may be selected from AEI, CHA, and AFX. In various embodiments, the zeolitic framework material is CHA.

In one or more embodiments, the SCR catalyst further comprises a metal, which may be a base metal. In various embodiments, the base metal, the noble metal, or a combination thereof may promote the catalytic activity of the zeolitic framework material.

In various embodiments, the selective catalytic reduction catalyst is promoted with a metal selected from Cu, Fe, Co, Ni, La, Ce, and Mn, and combinations thereof. In various embodiments, the selective catalytic reduction catalyst is promoted with a metal selected from Cu, Fe, and combinations thereof. In one or more embodiments, the zeolitic framework material is CHA promoted with copper and/or iron.

In embodiments with downstream SCR catalyst, low temperature lean NO_xTrap (LT-LNT) compositions store NO at temperatures below 300 ℃_xAnd thermally desorbing NO at a temperature above 300 ℃_x. According to one or more embodiments, the stored NO_xConversion to N under rich conditions below 300 ℃₂。

According to one or more embodiments, when the temperature of the SCR catalyst is adjusted to NO passing through the SCR catalyst_xWhen conversion is too low, a combined low temperature lean NO upstream of the SCR catalyst is utilized_xSystems of trap (LT-LNT) compositions are useful. In addition, low temperature lean NO when the SCR catalyst is activated at higher temperatures, such as greater than 300 deg.C_xTrap (LT-LNT) compositions adsorb low levels of NO_x. Thus, adding combined low temperature lean NO upstream of the SCR catalyst_xTrap (LT-LNT) trapping agents significantly improve the lower temperature activity of SCR systems.

It will be appreciated that such a system may also include a suitable reductant introduction system, such as an on-board aqueous urea storage reservoir storing a urea/water solution that is pumped to the urea injector by a pump containing a filter and a pressure regulator. The urea injector may include a nozzle upstream of the SCR catalyst that injects an atomized urea/water/air solution. Other suitable reductant introduction systems may include urea or cyanuric acid injectors that can meter solid particles of urea into a chamber heated by the exhaust gas to vaporize the solid reductant (sublimation temperatures range from about 300 to 400 ℃). Other nitrogen-based reductants particularly suitable for use in the control system of the present invention include cyanuramide, cyanuric diamide, ammonium cyanate, biuret, cyanuric acid, ammonium carbamate, melamine, tricyanourea, and mixtures of any number of these. However, the present invention is not limited to nitrogen-based reducing agents in its broader sense, but may include any reducing agent, including hydrocarbons, such as distillate fuels including alcohols, ethers, organo-nitro compounds and the like (e.g., methanol, ethanol, diethyl ether and the like) and various amines and salts thereof (particularly carbonates thereof), including guanidine, methyl carbonate, hexamethylamine and the like.

In another system embodiment, the low temperature lean NO described herein_xTrap (LT-LNT) compositions may be used in systems upstream of a Catalyzed Soot Filter (CSF) catalyst having a platinum group metal component. The CSF catalyst may be incorporated into or coated on a filter, for example a wall flow filter. Low temperature lean NO_xA trap (LT-LNT) composition is combined with the DOC composition described above. The LT-LNT in combination with the DOC can be placed upstream of the CSF, which, as described above, can be located upstream of the SCR catalyst with an upstream reductant injector. Thus, embodiments of the system will comprise a LT-LNT/DOC composition upstream of the PGM-catalyzed CSF upstream of the reductant injector and upstream of the SCR catalyst described above. In embodiments where the LT-LNT comprises Pt/Pd and a ceria component on a support comprising alumina, the Pt/Pd and ceria interaction on the alumina improves the ignition of the DOC. After filter regeneration, a short rich purge of about 5 seconds at 300 ℃ at 0.95 air to fuel ratio may be used. In an alternative embodiment, a LT-LNT with high CO and HC performance can be placed in a DOC formulation as a separate layer to introduce OBD functionality, and additionally for improving CO and HC light-off. However, in such embodiments, the engine must be rich (DenO) for activating the LT-LNT_x) Under the conditions.

In yet another system embodiment, a lean burn engine exhaust treatment system comprises a lambda sensor downstream of a LT-LNT in combination with a DOC composition. In one or more embodiments, the lambda sensor is in communication with an on-board diagnostic system. In one embodiment, the delay time of the lambda signal between two lambda sensors is measured. In one or more embodiments, one lambda sensor is upstream of the LT-LNT combined with the DOC composition and one lambda sensor is downstream of the LT-LNT combined with the DOC composition. The deterioration of the oxygen storage capacity of the DOC may be associated with deterioration of the hydrocarbon and carbon monoxide conversion of the LT-LNT/DOC catalyst when transitioning from lean to rich or from rich to lean. The lambda sensor used may be any suitable lambda sensor, for example, a Heated Exhaust Gas Oxygen (HEGO) or Universal Exhaust Gas Oxygen (UEGO) sensor.

The delay time or area between the ingress and egress signals can be measured. In the case of the delay time, the oxygen amount is given by the following formula:

OSC[mg]＝Δλ*Flow[kg/h]*Dt[s]*0.64 (1)，

where OSC [ mg ] is the mass of oxygen released by the oxygen storage component at the transition from lean to rich engine operating conditions, Δ λ is the difference in the λ values measured before and after the DOC, Flow represents the intake mass Flow, and Δ t is the time delay between the lambda jumps before and after the catalyst measured at the transition from lean to rich.

Alternatively, the lambda signal can be integrated to calculate the mass of oxygen stored per unit volume of catalyst using the following equation:

where ρ is_airIs the density of air, flow denotes the mass flow of the intake air, lambda_inAnd λ_outDenotes the lambda value measured before and after the DOC.

According to another embodiment of the invention, according to one or more implementationsThe LT-LNT/DOC catalyst described in the scheme is located upstream of a first hydrogen sensor, which measures H during the rich cycle₂Formed, which is used to scavenge the LT-LNT/DOC catalyst. OBD system monitors H measured by first hydrogen sensor₂The value is obtained. A target value determined from the Water Gas Shift (WGS) reaction is used to determine whether the OBD should provide a warning or alarm.

According to another embodiment of the invention, the LT-LNT/DOC catalyst described according to one or more embodiments is located at the first NH₃Upstream of the sensor, which measures NH during the rich cycle₃Formed, which is used to scavenge the LT-LNT/DOC catalyst. OBD system monitoring by first NH₃NH measured by sensor₃The value is obtained. According to by NO_xAnd H₂NH formed by reaction₃By a predetermined target NH₃The value determined target value is used to determine whether the OBD should provide a warning or alarm.

According to another embodiment of the invention, the LT-LNT/DOC catalyst according to one or more embodiments is located in the first NO_xUpstream of the sensor, which measures NO at low temperature during a lean period following a rich period_xStored to clean the catalyst. In particular, NO upstream of LT-LNT/DOC catalyst_xSensor and downstream NO_xSensor for measuring NO on LT-LNT/DOC catalyst_xAnd (5) storing. NO_xAdsorption amount and DOC for conversion of Hydrocarbons (HC), carbon monoxide (CO) and NO into NO₂Is relevant.

Additionally, in one or more embodiments, a first NO disposed downstream of the LT-LNT/DOC catalyst_xSensor with NO during rich periods_xSensor measuring NO_xSlipping to NO_xAfter storage the catalyst was washed at low temperature. Stored NO_xIs released and converted to N₂Associated with LT-LNT/DOC catalyst degradation. In particular, in NO_xAfter storage, application of enriched NO_xAnd (5) cleaning. Since it is not converted into N₂Released NO_xIn an amount corresponding to DOC for conversion of Hydrocarbons (HC), carbon monoxide (CO) and NO to NO₂Is relevant. OBD System monitorMeasuring the first NO_xNO measured by sensor_xThe value is obtained. NO based on leaving LT-LNT/DOC catalyst_xBy a predetermined target NO_xA target value for the value determination.

In one or more embodiments, a method of monitoring aging of a lean oxidation catalyst in a lean-burn engine catalyst system comprises passing a lean-burn engine exhaust gas stream of a diesel engine through a LT-LNT catalyst composition as described herein; measuring degradation of an LT-LNT composition located in the exhaust gas flow path; and correlating the degradation of the LT-LNT composition to a decrease in hydrocarbon conversion efficiency of the lean oxidation catalyst. In one or more embodiments, the lean burn engine catalyst system further comprises an Oxygen Storage Component (OSC). In one or more embodiments, the Oxygen Storage Component (OSC) is present in an amount sufficient such that a decrease in the oxygen storage capacity of the catalyst may be correlated with a deterioration in the ability of the diesel oxidation catalyst to convert hydrocarbons and/or carbon monoxide. The oxygen storage capacity of the OSC can be measured by applying a pulse of rich exhaust gas and determining the time delay of the lambda response measured before (upstream) and after (downstream) the Diesel Oxidation Catalyst (DOC). For example, when the DOC's ability to reduce hydrocarbons or carbon monoxide in the exhaust stream falls below some predetermined or preselected level, the delay time between measured lambda signals upstream and downstream of the catalyst will also decrease, as detected by the OBD system, due to the deterioration of oxygen storage capacity. The oxygen storage component may have a preselected deactivation temperature range that coincides with the deactivation temperature range of the precious metal component at which the hydrocarbon conversion of the precious metal component decreases below a preselected value. Thus, this correlation can be achieved by calibrating the deterioration of the OSC and the deterioration of the diesel catalyst performance. The OBD system may then provide a signal or alert to the vehicle operator indicating that exhaust system maintenance is required. In one or more embodiments, the interaction of PGM with a reducible metal oxide, such as a ceria compound, is produced by adding PGM-impregnated alumina to a slurry with a reducible metal oxide. The slurry was subsequently ground to a particle size d90 of 9 μm. The final slurry is then coated onto a metal flow-through substrate. Thus, the interaction between the PGM and the OSC is not a direct interaction by impregnating the reducible metal oxide with the PGM but an indirect interaction by grinding the PGM and the OSC in the slurry.

In a reducing environment, lean in NO_xThe trap (LNT) activates a reaction by promoting a steam reforming reaction and a Water Gas Shift (WGS) reaction of hydrocarbons to provide hydrogen (H)₂) As reducing agents for reducing NO_x. The water gas shift reaction is a chemical reaction in which carbon monoxide reacts with steam to form carbon dioxide and hydrogen. In one or more embodiments, the step of measuring degradation of the LT-LNT composition comprises monitoring H in the exhaust gas stream during a rich purge with a lambda sensor at 250 ℃₂And (4) content. In one or more embodiments, the first lambda sensor may be located upstream of a Diesel Oxidation Catalyst (DOC) and the second lambda sensor may be located downstream of the DOC. According to one or more embodiments, the first λ sensor and the second λ sensor are in communication with an on-board diagnostic system (OBD). In one or more embodiments, the DOC can provide an OBD function, wherein a delay time of the lambda signal between a first lambda sensor located upstream of the DOC and a second lambda sensor located downstream of the DOC can be used to measure degradation of an oxygen storage component located in the exhaust flow path; and correlating the degradation of the Oxygen Storage Catalyst (OSC) with a decrease in hydrocarbon conversion efficiency. Deterioration of the OSC may be associated with CO/HC deterioration when switching from lean to rich or from rich to lean.

In one or more embodiments, the step of measuring the degradation of the LT-LNT composition comprises measuring the degradation of the LT-LNT composition with NH₃Monitoring NH of exhaust flow during sensor rich purge₃And (4) content. By NH₃Sensor measurement as NO_xAnd H₂As a result of the reaction of (1), NH of DOC during the enrichment treatment₃And (4) forming. H occurs during rich purge₂As formed, the lambda signal downstream of the DOC is below the target value (from the WGS reaction).

In one or more embodiments, the method of monitoring the aging state of a lean burn oxidation catalyst in a lean burn engine catalyst system further comprises activating an alarm when the hydrocarbon conversion efficiency falls below a preselected value.

The invention will now be described with reference to the following examples. Before describing several exemplary embodiments of the invention, it is to be understood that the invention is not limited to the details of construction or process steps set forth in the following description. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.

Examples

Effect of Rh and PGM Supports

1.1 examples 1.1 to 1.3-LT-LNT vs. DOC and Rh

As shown in table 1 below, the DOC is referred to as sample 1.1 and represents a sample of a prior art DOC. LT-LNT a is referred to as sample 1.2 and represents a sample of the LNT of the invention. LT-LNT B is referred to as sample 1.3 and also represents a sample of the LNT of the invention.

TABLE 1

Matrix 5.66 by 4 "400/4

Sample 1.1 prior art DOC

To prepare the first (bottom) layer of sample 1.1, a palladium nitrate solution was added at 0.75g/in³In the high-porosity gamma-alumina, 22g/ft is obtained³Pd. The resulting frit was dispersed in water and acid (e.g., acetic acid) and milled to a particle size d90 of 25 microns. 0.75g/in³OSC material (ZrO)₂: 43.5 wt.% CeO₂: 45% by weight of La₂O₃8% by weight, Pr₆O₁₁: 2% by weight of HfO₂: 1.5 wt.%) was dispersed in the slurry and ground to a particle size d90 of 7 microns. The final slurry was coated onto the monolith, air dried at 110 ℃ and calcined in air at 590 ℃. To prepare the second (intermediate) layer of sample 1.1, 1.5g/in was impregnated with an aqueous solution of palladium nitrate³To a final dry of 30g/ft³Pd content of (a). The resulting powder was dispersed in water. The platinum solution with platinum was added as an ammine stabilized hydroxypt IV complex to give 60g/ft³Dry content of. After adjusting the pH of the slurry to 4.5, the slurry was ground to a particle size d90 of 16 μm. The slurry was then subsequently coated onto the first layer, air dried at 110 ℃ and calcined in air at 590 ℃.

To prepare the third (top) layer of sample 1.1, 0.25g/in was added³High porosity gamma-alumina and 0.5g/in³OSC material (ZrO)₂：43.5wt％，CeO₂：45wt％，La₂O₃:8wt％，Pr₆O₁₁: 2% by weight of HfO₂: 1.5%) were mixed and impregnated with an aqueous palladium nitrate solution to give a final 8g/ft³Dry Pd content of. The impregnated material is then dispersed in water and acid (e.g. acetic acid) and milled to a particle size d90 of 20 microns. 0.5g/in³The H-beta zeolite was immersed in water to a solids content of 45%. The noble metal-containing slurry was mixed with the H- β slurry, milled to a particle size d90 of 15 μm, and subsequently coated on the second layer, air dried at 110 ℃ and calcined in air at 590 ℃.

Sample 1.2LT-LNT (inventive)

To prepare sample 1.2, which is an embodiment of the present invention, a platinum solution with platinum was first impregnated at 3g/in with an ammine-stabilized hydroxypt IV complex³To obtain 51g/ft of high-porosity gamma-alumina³And then impregnated with an aqueous palladium nitrate solution to give a final 4.5g/ft³The dry Pd content of (A) is as follows. The resulting powder, having a solids content of 65-70%, was dispersed in water. To this slurry was added 100% ceria material (1.1 g/in)³) (ii) a Magnesium acetate 4 hydrate (0.3 g/in) was added³) And zirconium acetate (0.05 g/in)³). The resulting slurry was ground to a particle size d90 of 9 μm. The final slurry is then coated into a ceramic flow-through substrate. The coated substrate was dried in air at 110 ℃ and calcined in air at 590 ℃.

Sample 1.3LT-LNT (inventive)

To prepare sample 1.3, which is one embodiment of the present invention, a platinum solution with platinum was first impregnated at 3g/in with an ammine-stabilized hydroxypt IV complex³To obtain 51g/ft of high-porosity gamma-alumina³Dry Pt content of (2), secondly with nitric acidImmersion in an aqueous palladium solution to give 4.5g/ft³Final dry Pd content. The resulting powder, having a solids content of 65-70%, was dispersed in water.

For Rh impregnation, 100% ceria material (0.3 g/in)³) Dispersed in water to a solids content of 43%. Rh nitrate solution was added to ceria slurry to give 4.5g/ft³Final dry Rh content.

The resultant Rh/ceria slurry, 100% ceria material (0.8 g/in)³) Magnesium acetate 4 hydrate (0.3 g/in)³) And zirconium acetate (0.05 g/in)³) Added to the Pt/Pd/alumina slurry. The slurry was subsequently ground to a particle size d90 of 9 μm. The final slurry is then coated into a ceramic flow-through substrate. The coated substrate was dried in air at 110 ℃ and calcined in air at 590 ℃.

New European Drive Cycle (NEDC) CO and HC Performance evaluation

Samples 1.1-1.3 were tested on an engine test unit equipped with a european 62L engine with 3 standard new european driving cycle operations (NEDC). Samples 1.1-1.3 were aged at 750 ℃ for 15 hours under a stream of air with 10% water vapor prior to testing. In the case of the LT-LNT of samples 1.2 and 1.3, rich engine mode 7s was applied at λ 0.95 at 1075s point in NEDC. The CO and HC conversions of the samples were measured as shown in table 2. The average temperature of the first 4 ECE cycles was 120 ℃. Higher conversion rates show better gas activity.

TABLE 2 NEDC Engine emissions and conversions for the third test cycle

As shown in table 2, the CO performance of the low PGM loaded LT-LNT of samples 1.2 and 1.3 has comparable performance compared to DOC (sample 1.1), with about twice the amount of PGM. The HC performance of the DOC is higher due to the zeolite in the formulation.

For DeNO_xLean/rich cycle test for (de-NOx) performance evaluation

For DenO_xPerformance evaluation, using lean/rich cycle test. The lean/rich cycle test is an engine test consisting of 7 lean/rich cycles performed at 7 different pre-catalyst temperatures of 190 ℃ to 500 ℃. For each temperature at the start of the experiment, a 30 second rich run was performed to ensure that all nitrates were desorbed from the LT-LNT. During lean periods, engine-out NO_xStored on LT-LNT catalyst. After the lean phase, the engine enters rich mode for 10-15 seconds. In rich mode, most of the stored NO on the catalyst_xConverted to nitrogen. Monitoring and evaluation of mean NO for the last 5 cycles_xConversion and NO during the last 5 cycles of the rich phase_xAnd (5) discharging. FIGS. 1 and 2 show NO for 16h hydrothermal oven aged samples 1.2 and 1.3_xConversion and NO_xAnd breaking through. Rh in sample 1.3 reduced NO during the rich phase at temperatures below 300 deg.C_xThus increasing NO in this temperature range_xAnd (4) conversion rate.

1.2 examples 1.4 and 1.5-PGM sites

As shown in table 3 below, LT-LNT C is referred to as sample 1.4, representing a sample of an LNT of the present invention. LT-LNT D is referred to as sample 1.5 and also represents a sample of prior art LNT.

TABLE 3

Matrix 5.66 × 4.5 "400/4

Sample 1.4LT-LNT (inventive)

To prepare sample 1.4, which is an embodiment of the present invention, a platinum solution with platinum was first impregnated at 2g/in with an ammine-stabilized hydroxypt IV complex³To obtain 51g/ft of high-porosity gamma-alumina³Is then impregnated with an aqueous palladium nitrate solution to give a final 4.5g/ft³Dry Pd content of. The resulting powder, having a solids content of 65-70%, was dispersed in water. To this slurry was added 100% ceria material (2.25 g/in)³) (ii) a Magnesium acetate 4 hydrate (0.3 g/in) was added³) And zirconium acetate (0.05 g/in)³) And areAnd (4) mixing. The resulting slurry was ground to a particle size d90 of 9 μm. Mixing H-beta zeolite material (0.5 g/in)³) Added to the milled slurry. The final slurry is then coated into a ceramic flow-through substrate. The coated substrate was dried in air at 110 ℃ and calcined in air at 590 ℃.

Sample 1.5 prior art LT-LNT (comparative)

To prepare sample 1.5, which represents a sample of the prior art LT-LNT, a 2.25g/in platinum solution with platinum was first impregnated with an ammine-stabilized hydroxypival IV complex³To give 51g/ft of ceria material³Then impregnated with an aqueous palladium nitrate solution to give 4.5g/ft³Final dry Pd content. The resulting powder, having a solids content of 65-70%, was dispersed in water. To this slurry was added highly porous gamma alumina (2.0 g/in)³) (ii) a Magnesium acetate 4 hydrate (0.3 g/in)³) And zirconium acetate (0.05 g/in)³) And mixed. The resulting slurry was ground to a particle size d90 of 9 μm. Mixing H-beta zeolite material (0.5 g/in)³) Added to the milled slurry. The final slurry is then coated into a ceramic flow-through substrate. The coated substrate was dried in air at 110 ℃ and calcined in air at 590 ℃.

Ignition test for CO and HC Performance testing

Samples 1.2, 1.4 and 1.5 were tested for ignition performance on an engine test unit. Prior to testing, the samples were first aged at 750 ℃ for 15 hours under a stream of air with 10% water vapor, and then activated on the engine at 300 ℃ for 10 seconds by a rich lambda purge. For the ignition test, each sample was placed downstream of the exhaust line of a 6 cylinder light diesel engine with a 3 liter displacement. The CO and HC concentrations in the exhaust gas stream were constant at 1250ppm and 200ppm (C), respectively₃Reference). Gas flow rate under standard conditions is about 45m³H is used as the reference value. The temperature ramp was 2 deg.C/min.

Lower ignition temperatures are indicative of better gas activity.

As shown in fig. 3 and 4, the LT-LNT with Pt/Pd impregnated on ceria (sample 1.5) showed significantly lower CO and HC performance compared to the corresponding LT-LNT with Pt/Pd impregnated on alumina support (sample 1.4). The incorporation of zeolite improves the HC performance of LT-LNT.

1.3 examples 1.6 and 1.11-alumina: ceria ratio, Ba and support variations, and LNT

TABLE 4

Substrate 4.5 ANGSTROM 5.4' 300/600 Metal substrate

Sample 1.6LT-LNT (inventive)

To prepare sample 1.6, which represents a sample of LT-LNT B of the invention, first a 3g/in solution of platinum with platinum as an ammine-stabilized hydroxypt IV complex was impregnated³To obtain 130g/ft of high-porosity gamma-alumina³And then impregnated with an aqueous palladium nitrate solution to give a final 15g/ft³Dry Pd content of. The resulting powder, having a solids content of 65-70%, was dispersed in water.

For Rh impregnation, 100% ceria material (0.3 g/in)³) Dispersed in water to a solids content of 43%. Rh nitrate solution was added to the ceria slurry to give 5g/ft³Final dry Rh content.

The resultant Rh/ceria slurry, 100% ceria material (0.8 g/in)³) Magnesium acetate 4 hydrate (0.3 g/in)³) And zirconium acetate (0.05 g/in)³) Added to the Pt/Pd/alumina slurry. The slurry was subsequently ground to a particle size d90 of 9 μm. The final slurry is then coated onto a metal flow-through substrate. The coated substrate was dried in air at 110 ℃ and calcined in air at 590 ℃.

Sample 1.7LT-LNT (inventive)

To prepare sample 1.7, which represents a sample of LT-LNT E of the invention, first 1.8g/in of a platinum solution with platinum as an ammine-stabilized hydroxypt IV complex was impregnated³High pore gamma-alumina to yield 130g/ft³Pt dry content, followed by impregnation with aqueous palladium nitrate solution to give 15g/ft³Final dry Pd content. The obtained solidThe powder with a content of 65-70% is dispersed in water.

For Rh impregnation, 100% ceria material (0.4 g/in)³) Dispersed in water to a solids content of 43%. Rh nitrate solution was added to the ceria slurry to give 5g/ft³Final dry Rh content.

The resultant Rh/ceria slurry, 100% ceria material (2.85 g/in)³) Magnesium acetate 4 hydrate (0.3 g/in)³) And zirconium acetate (0.05 g/in)³) Added to the Pt/Pd/alumina slurry. The slurry was subsequently ground to a particle size d90 of 9 μm. The final slurry is then coated onto a metal flow-through substrate. The coated substrate was dried in air at 110 ℃ and calcined in air at 590 ℃.

Sample 1.8LT-LNT (inventive)

To prepare sample 1.8, which represents a sample of LT-LNT F of the invention, first 1.8g/in of a platinum solution with platinum as an ammine-stabilized hydroxypt IV complex was impregnated³To obtain 130g/ft of high-porosity gamma-alumina³And then impregnated with an aqueous palladium nitrate solution to give 15g/ft³Final dry Pd content. The resulting powder, having a solids content of 65-70%, was dispersed in water.

For Ba impregnation on ceria, an aqueous solution of BaOAC (0.05 g/in) was used³) Dipping 2.85g/in³100% of a ceria material. The resulting powder was calcined at 590 ℃ for 2 hours to yield a Ba/ceria material with a BaO content of 1.7%.

To the Pt/Pd/alumina slurry was added Rh/ceria slurry, Ba/ceria material (2.9 g/in)³) Magnesium acetate 4 hydrate (0.3 g/in)³) And zirconium acetate (0.05 g/in)³). The slurry was subsequently ground to a particle size d90 of 9 μm. The final slurry is then coated onto a metal flow-through substrate. Drying the coated substrate in air at 110 deg.C and calcining at 590 deg.C in airAnd (6) burning.

Sample 1.9LT-LNT (inventive type)

To prepare sample 1.9, which represents a sample of LT-LNT G of the invention, first 1.8G/in of a platinum solution with platinum as the ammine-stabilized hydroxypt IV complex was impregnated³To obtain 130g/ft of high-porosity gamma-alumina³And then impregnated with an aqueous palladium nitrate solution to give 15g/ft³Final dry Pd content. The resulting powder, having a solids content of 65-70%, was dispersed in water.

For Rh impregnation, 100% ceria material (0.4 g/in)³) Dispersed in water to a solids content of 43%. The Rh nitrate solution was added to the ceria slurry to give a final dry Rh content of 5g/ft³。

For Ba impregnation on ceria, an aqueous solution of BaOAC (0.15 g/in) was used³) Dipping 2.85g/in³100% of a ceria material. The resulting powder was calcined at 590 ℃ for 2 hours to yield a Ba/ceria material with 5% BaO content.

Rh/ceria slurry, Ba/ceria material (3 g/in) was added to Pt/Pd/alumina slurry³) Magnesium acetate 4 hydrate (0.3 g/in)³) And zirconium acetate (0.05 g/in)³). The slurry was subsequently ground to a particle size d90 of 9 μm. The final slurry is then coated onto a metal flow-through substrate. The coated substrate was dried in air at 110 ℃ and calcined in air at 590 ℃.

Sample 1.10LT-LNT (inventive type)

To prepare sample 1.10, which represents a sample of LT-LNT H of the present invention, first 1.3g/in of a platinum solution with platinum as an ammine-stabilized hydroxypival IV complex was impregnated³To obtain 130g/ft of high-porosity gamma-alumina³And then impregnated with an aqueous palladium nitrate solution to give 15g/ft³Final dry Pd content. The resulting powder, having a solids content of 65-70%, was dispersed in water.

The resultant Rh/ceria slurry, 100% ceria material (3.4 g/in)³) Magnesium acetate 4 hydrate (0.3 g/in)³) And zirconium acetate (0.05 g/in)³) Added to the Pt/Pd/alumina slurry. The slurry was subsequently ground to a particle size d90 of 9 μm. The final slurry is then coated onto a metal flow-through substrate. The coated substrate was dried in air at 110 ℃ and calcined in air at 590 ℃.

Sample 1.11LT-LNT (inventive type)

To prepare sample 1.11, which represents a sample of LT-LNT I of the present invention, 4.7g/in of platinum solution with platinum was first impregnated with ammine-stabilized hydroxypt IV complex³Of Ce/Al (50%/50%) material, to yield 130g/ft³And then impregnated with an aqueous palladium nitrate solution to give 15g/ft³Final dry Pd content. The resulting powder, having a solids content of 65-70%, was dispersed in water.

The resultant Rh/ceria slurry, magnesium acetate 4 hydrate (0.3 g/in)³) And zirconium acetate (0.05 g/in)³) Added to the Pt/Pd/alumina slurry. The slurry was subsequently ground to a particle size d90 of 9 μm. The final slurry is then coated onto a metal flow-through substrate. The coated substrate was dried in air at 110 ℃ and calcined in air at 590 ℃.

Sample 1.12 prior art LNT (comparative)

To prepare the first (bottom) layer of sample 1.12, 2.45g/in was first impregnated with a platinum solution with platinum as an ammine-stabilized hydroxypt IV complex³Ba/Ce/alumina (20/13/67) to obtain 90g/ft³And then impregnated with an aqueous palladium nitrate solution to give 15g/ft³Final dry Pd content. The resulting powder, having a solids content of 65-70%, was dispersed in water.

Adding 100 percent of the catalyst into Pt/Pd/Ba/Ce/alumina slurryCeria (2.45 g/in)³) Magnesium acetate 4 hydrate (0.3 g/in)³) And zirconium acetate (0.05 g/in)³). The slurry was subsequently ground to a particle size d90 of 9 μm. The final slurry is then coated onto a metal flow-through substrate. The coated substrate was dried in air at 110 ℃ and calcined in air at 590 ℃.

To prepare the second (top) layer of sample 1.12, first 0.7g/in of a platinum solution with platinum as an ammine-stabilized hydroxypt IV complex was impregnated³To obtain 40 g/ft of high-porosity gamma-alumina material³Pt dry content of (a). The resulting powder, having a solids content of 55-60%, was dispersed in water.

For Rh impregnation, 100% ceria material (0.5 g/in)³) Dispersed in water to a solids content of 43%. Rh nitrate solution was added to the ceria slurry to give 5g/ft³Final dry Rh content.

The resultant Rh/ceria slurry was added to the Pt/Pd/alumina slurry. The slurry was subsequently ground to a particle size d90 of 8 μm. The final slurry is then coated onto a metal flow-through substrate. The coated substrate was dried in air at 110 ℃ and calcined in air at 590 ℃.

Lean/rich DeNO_xPerformance evaluation cycle test

For DenO_xPerformance evaluation, using lean/rich cycle test. The lean/rich cycle test is an engine test consisting of 7 lean/rich cycles performed at 7 different catalyst temperatures from 200 ℃ to 500 ℃. For each temperature at the start of the experiment, a 30 second rich run was performed to ensure that all nitrates were desorbed from the LT-LNT. During lean periods, engine-out NO_xStored on LT-LNT catalyst. After the lean phase, the engine enters rich mode for 10-15 seconds. In rich mode, most of the stored NO on the catalyst_xConverted to nitrogen. As shown in FIGS. 5 and 6, the average NO of samples 1.6-1.9 and sample 1.11 at the last 5 cycles of the 7-cycle lean-rich test was monitored and evaluated_xConversion and NO during the last 5 cycles of the rich phase_xAnd (5) discharging. LT-LNT was hydrothermally aged at 800 ℃ for 16h in an oven.

As shown in fig. 5, canNO at low temperature with increased Ba loading in LT-LNT_xThe conversion is improved and the temperature range of the LT-LNT is expanded to higher temperatures. As shown in FIG. 6, the lower ceria to alumina ratio in LT-LNT improves NO in the low temperature range_xAnd (4) conversion rate.

World light harmony test cycle (WLTC) -DeNO_xEvaluation of CO and HC Performance

Samples were tested with downstream SCR filter (scruf) technology at an engine test unit with a standard WLTC procedure. The test unit was equipped with a Euro 51.6L engine with continuous dosing of urea upstream of the SCREF, with ammonia and NO_xIs 1.2 (NSR). The average temperature of the first 1000s of the WLTC cycle was 135 ℃. The SCREF technology is the currently available Cu-SCR technology. Prior to testing, samples were aged at 800 ℃ for 16 hours under an air stream with 10% water vapor, or at 690 ℃ at LT-LNT bed temperature for 16 hours under an air stream with 40 standard DeSOx events. In the case of the LNT and LT-LNT, rich engine mode is applied at 5 different locations in the cycle at λ 0.95 during WLTC. Measuring NO of sample_xCO and HC conversion. Higher conversion indicates better gas activity. Table 5 shows the conversion after furnace aging after a treatment system with DOC or LT-LNT with a downstream scref with a third WLTC, with the emissions upstream of the catalyst system as follows: NO_x＝0.335g/km； CO＝1.7g/km；HC＝0.225g/km)。

As shown in Table 5, NO for LT-LNT systems with prior art Cu-SCR technology (samples 1.7 and 1.10) compared to DOC based systems (sample 1.1)_xCO and HC conversion is significantly higher.

TABLE 5

Sample (I)	NO_xConversion rate/%	CO conversion/%	HC conversion/%
				1.1DOC (comparison)	46	60	73
1.7LT-LNT (inventive)	60	86	79
				1.10LT-LNT (inventive)	65	93	82

Table 6 shows the conversion of the denox aging system with LNT or LT-LNT with a downstream scref with a third trial WLTC, with the emissions upstream of the catalyst system as follows: NO_x0.290 g/km; CO is 1.7 g/km; HC is 0.220 g/km. As shown in Table 6, the LT-LNT based system (sample 1.7) showed comparable NO compared to the prior art LNT based system (sample 1.12)_xConversion and higher CO and HC conversions.

TABLE 6

Sample (I)	NO_xConversion rate/%	CO conversion/%	HC conversion/%
				1.12LNT (comparative)	67	72	69
1.7LT-LNT (inventive)	66	84	77

In the present specification, "one embodiment," "certain embodiments," "one or more embodiments" or "an embodiment" means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, appearances of the phrases such as "in one or more embodiments," "in certain embodiments," "in one embodiment," or "in an embodiment" in various places throughout this specification are not necessarily referring to the same embodiment of the invention. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments. The order of description of the above methods should not be construed as a limitation, and methods may use the described operations out of order or with omissions or additions.

It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of ordinary skill in the art upon reading the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims

1. A lean burn engine exhaust treatment article comprising:

low temperature NO lean comprising washcoat on carrier substrate_xA trap (LT-LNT) composition,

wherein the washcoat comprises:

a platinum compound, a palladium compound, or a combination thereof impregnated on a first support material comprising ceria, alumina, or a combination thereof,

a rhodium compound impregnated on a second support material comprising ceria, and

low temperature NO comprising ceria optionally impregnated with 1-10% barium compound_xThe storage material is stored in a storage container,

wherein the washcoat on the carrier substrate consists of one layer.

2. The lean burn engine exhaust gas treatment article of claim 1, wherein the platinum, palladium, or combination thereof is not directly impregnated with low temperature NO_xOn the storage material.

3. The lean burn engine exhaust treatment article of claim 1, wherein the first support material comprises 100% alumina.

4. The lean burn engine exhaust treatment article of claim 1, wherein the first support material consists essentially of ceria and alumina.

5. The lean burn engine exhaust treatment article of claim 4, wherein the first support material comprises 20 to 50 wt% ceria and 50 to 80 wt% alumina.

6. The lean burn engine exhaust treatment article of claim 4, wherein the ceria and alumina are present at a ceria to alumina ratio of 30: 70.

7. The lean burn engine exhaust treatment article of claim 4, wherein the ceria and alumina are present at a ceria to alumina ratio of 50: 50.

8. The lean burn engine exhaust treatment article of claim 1, wherein low temperature NO_xThe storage material comprises 100% ceria.

9. The lean burn engine exhaust treatment article of claim 1, wherein the first support material further comprises at least one dopant selected from the group consisting of oxides of La, Zr, Nb, Pr, Y, Nd, and Sm.

10. The lean burn engine exhaust treatment article of claim 1, wherein the washcoat comprises a combination of platinum and palladium.

11. The lean burn engine exhaust treatment article of claim 10, wherein the alumina and ceria are present in the LT-LNT composition in an alumina to ceria ratio of 4:1 to 1: 4.

12. The lean burn engine exhaust treatment article of claim 11, wherein the alumina and ceria are present in the LT-LNT composition in an alumina to ceria ratio of 1:1 to 1: 4.

13. The lean burn engine exhaust treatment article of claim 12, wherein the alumina and ceria are present in the LT-LNT composition in an alumina to ceria ratio of 1:1 to 1: 3.

14. The lean burn engine exhaust gas treatment article of claim 11, wherein the LT-LNT composition is disposed as a washcoat on a substrate and the alumina is at 1 to 4g/in³A range of (a) exists.

15. The lean burn engine exhaust treatment article of claim 10, wherein the LT-LNT composition comprises at greater than 0 to 20g/ft³Rh present on the second support.

16. The lean burn of claim 15An engine exhaust treatment article wherein the LT-LNT composition comprises at least 2 to 10g/ft³Rh present on the second support.

17. The lean burn engine exhaust gas treatment article of claim 16, wherein the LT-LNT composition comprises at 3 to 7g/ft³Rh present on the second support.

18. The lean burn engine exhaust treatment article of claim 15, wherein the platinum is present at 20 to 200g/ft³In the range of 1 to 50g/ft of palladium³A range of (a) exists.

19. The lean burn engine exhaust treatment article of claim 1, wherein the LT-LNT composition is free of barium and other alkaline earth metals.

20. The lean burn engine exhaust gas treatment article of claim 1, wherein the LT-LNT composition further comprises 1 to 10 wt% of an alkaline earth metal selected from the group consisting of Mg, Ca, Sr and Ba.

21. The lean burn engine exhaust treatment article of claim 20, wherein the alkaline earth metal is Mg and Ba.

22. The lean burn engine exhaust treatment article of claim 20, wherein the alkaline earth metal is Ba.

23. A lean burn engine exhaust treatment system comprising the lean burn engine exhaust treatment article of claim 1 and a downstream Selective Catalytic Reduction (SCR) catalyst.

24. The lean burn engine exhaust gas treatment system of claim 23, wherein the LT-LNT composition is disposed as a washcoat on a substrate and the SCR catalyst is disposed as a separate washcoat on a separate downstream substrate.

25. The lean burn engine exhaust gas treatment system of claim 24, wherein the LT-LNT composition is on a honeycomb flow-through substrate and the SCR catalyst is on a wall-flow substrate.

26. The lean burn engine exhaust gas treatment system of claim 24, wherein the LT-LNT composition is on a wall flow substrate and the SCR catalyst is on a honeycomb flow-through substrate.

27. A lean burn engine exhaust treatment system comprising the lean burn engine exhaust treatment article of claim 1 and a lambda sensor downstream of the LT-LNT.

28. The lean exhaust system of claim 27, further comprising a second lambda sensor positioned upstream of the LT-LNT, and the lambda sensor and the second lambda sensor are in communication with an on-board diagnostic system that correlates a worsening of the oxygen storage capacity of the LT-LNT to a worsening of the HC conversion rate of the LT-LNT.